Continuous Process For On Site And On Demand Production Of Aqueous Peracetic Acid

ABSTRACT

Peracetic acid is prepared on-site and on-demand in a continuous process and at a controlled rate to meet the demand of a downstream operation. In one aspect, a continuous tank reactor is used to produce quantities of peracetic acid at a controlled rate in liquid or vapor form. In another aspect, the use of super acid catalysts enhances the production of peracetic acid under milder conditions, for example, than those typically encountered when using sulfuric acid catalysts alone.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 10/900,209, filed Jul. 28, 2004, now U.S. Pat. No. 7,012,154 B2, the disclosure of which is hereby incorporated by reference.

BACKGROUND

Peracetic acid (sometimes referred to as PAA or HOOAc) has long been recognized for its utility in a wide variety of end uses. In water and wastewater disinfection, for example, PAA destroys microorganisms and pathogens harmful to the public and the environment without producing toxic by-products or leaving chemical residuals. In bleaching applications, PAA yields higher levels of brightness without degrading fiber strength. Other applications, including equipment sanitizing, grain and soil sterilization, and chemical synthesis profit from the benefits of PAA over the alternatives.

Currently, PAA is produced commercially as an equilibrium mixture of hydrogen peroxide, acetic acid, water, and sulfuric acid with trace amounts of stabilizers. The active peracetic acid content is controlled from 5 to 50%, by weight, depending on the particular end use. The use of equilibrium PAA (eq-PAA) is limited by its inherent instability and safety considerations, particularly at high concentrations. For example, 35% solutions are flammable under the National Fire Prevention Association (NFPA) standards. Commercial transport regulations restrict the concentration to less than 35% when shipped over public avenues, however, manufacturers typically limit the concentration to 15% except for special circumstances. Higher concentrations require on-site production by the end user.

Equilibrium PAA is economic disadvantages over pure peracetic acid due to the lost costs of unreacted raw materials contained in the finished product. Separation of the unreacted materials from the eq-PAA to obtain only aqueous PAA is not practical since the resulting mixture exhibits an extremely short shelf life (hours). The short shelf life is due to the PAA quickly reaching new equilibrium conditions containing much less active PAA.

There are many applications where the nature of eq-PAA mixtures discourages its use. For example, in conventional wastewater treatment plants, the unreacted hydrogen peroxide (H₂O₂) and acetic acid (HOAc) will contribute significantly to the loading properties in final discharges, including Chemical Oxidation Demand (COD), Biochemical Oxygen Demand (BOD), and Total Organic Carbon (TOC), etc. The excess sulfuric acid (H₂SO₄) and HOAc may also require additional pH adjustment, all of which must meet local and federal discharge permits (for example NPDES, National Pollutant Discharge Elimination System) promulgated under the U.S. Clean Water Act.

Several methods have been proposed to produce PAA without the deleterious effects from residual reactants, catalysts, and other impurities associated with conventional eq-PAA. Among these are acid neutralization, reaction media sparging, adding stabilizers, and distillation. In applications using eq-PAA for its active PAA content, the residual reactants and catalyst generally are not utilized and therefore wasted, leading to cost inefficiencies.

In acid neutralization, the remaining sulfuric acid and acetic acid are neutralized. One example of acid neutralization process is found in U.S. App. No. 2002/0193626 to Pohjanvesi et al., which describes using a base to neutralize the unreacted acids whereby the PAA is stabilized. Acid neutralization processes generally require the dilution of PAA by the addition of a stoichiometric equivalent amount of a base and the introduction of conjugate salts that are not desirable in most applications.

In reaction medium sparging, fresh acid catalyst is fed continuously into the reaction medium while withdrawing a similar volume continuously to purify the medium of impurities threatening the safety of the process. One example of medium sparging is found in U.S. App. No. 2002/0177732 to Pohjanvesi, et al., which describes feeding a catalyst continuously into the reaction medium by withdrawing a portion of the medium as a bottom product. The resulting medium is distilled into PAA in an aqueous solution. This method generates hazardous waste that must be disposed of, increasing the costs of production.

Literature describing the technology for the continuous production of distilled peracetic acid has been available since the 1950's. To date, only limited use of this technology has been made, and only on a large commercial scale. The principal hazard associated with the use of this unrefined technology is the potential for unstable conditions to exist within the vapor space above the surface of the liquid in the reactor. The processes are designed for large scale production of PAA using large quantities of reacting solutions and large head spaces above the solution at the base of the distillation column.

One example of a distillation process is found in U.S. Pat. No. 5,886,217 to Pudas, which describes the production of eq-PAA and distilling off PAA in aqueous solution continuously based on the amount of thermal energy applied to the reaction medium. Pudas seeks to produce the maximum yield of PAA by increasing or maintaining a high level of thermal energy input through the use of a heat exchanger circulating device. The heat exchanger circulating device circulates the reaction medium up to 200 times per hour and basically serves only as a continuously mixed reactor and heater. The shear stresses and turbulence associated with this mixing can cause the reactants and products to decompose prematurely, reducing the yield and efficiency of the process. The method is not responsive to the demand of the end use applications. In addition, inventories of reactive material and stored product typically are large, which aggravates safety and hazard risk concerns.

Another example of distillation is shown in E.P. App. 98203946.3, which describes the use of stabilizers and chillers to stabilize PAA. This process is more expensive and complex due to extensive refrigeration equipment and large inventory storage requirements. In addition, the large inventory storage increases safety concerns.

In U.S. Pat. No. 5,122,538 to Lokkesmore et al., a method is disclosed to produce equilibrium peracetic acid products on-site at the point of use. The method utilizes a non-swelling acid exchange resin as a catalyst to produce peracetic acid from acetic acid and hydrogen peroxide. The equilibrium peracetic acid product contains substantial amounts of acetic acid and hydrogen peroxide. The prolonged equilibration time (normally several hours) necessitates large inventories of peracetic acid, which present storage hazards requiring special precautions.

In E.P. 0 789 016 B1 to Pudas, a method is disclosed for producing peracetic acid by reacting hydrogen peroxide and acetic acid in an aqueous medium that is continuously supplied with more than 0.2 KW/kg of thermal energy while the peracetic acid produced is continuously separated and removed by distillation. The reaction medium circulates in the heating device with the aid of a pump which increased the pressure of the reaction medium to allow temperature rise with boiling in the circulation loop.

In E.P. 1 004 576 A1 to Bloomfield, a method for producing peracetic acid involves reacting hydrogen peroxide and acetic acid in an aqueous medium in the presence of an acid catalyst and continuously distilling off the peracetic acid. The molar ratio of hydrogen peroxide to acetic acid ranges from 0.6:1 to 4:1, respectively. The reaction medium circulates through a thermosyphon reboiler by natural convection boiling.

E.P. 1 247 802 B1 to Pohjanvesi et al. discloses a method for neutralizing the small reactor purge stream and combining with the distilled peracetic acid to eliminate a waste stream and achieve slightly better utilization of the raw materials.

In Swern, D., “Organic Peroxides”, Vol. 1, John Wiley & Sons, New York, 1970, pp. 349-351, a process is described for the production of peracetic acid by distilling off peracetic acid from an aqueous reaction medium containing acetic acid, hydrogen peroxide, peracetic acid, and sulfuric acid catalyst in substantial equilibrium.

Many processes have used various types of catalysts in efforts to increase reaction rates in the production of PAA. For example, U.S. App 2004/0245116 to Ohsaka discloses solid support catalysts containing sulfonated polystyrenes and sulfonated tetrafluoroethylene ethers (specifically tetrafluoroethylene-perfluoro[2-(fluorosulfonyl-ethoxy)-propyl]vinylether (Nafion®, referred to herein as sulfonated tetrafluoroethylenes) in an electrolytic cell. A sterilizing/cleaning apparatus uses a peroxide having an electrolytic cell for performing electrolysis while being supplied with acetic acid and or acetate and an oxygen-containing gas to synthesize an aqueous solution containing peracetic acid and hydrogen peroxide.

Lokkesmoe U.S. Pat. No. 5,122,538 discloses a solid super acid containing sulfonated polystyrene divinyl benzene copolymer to produce peracetic acid in the presence of hydrogen peroxide and acetic acid. This catalyst requires a chelating agent to prevent swelling and fouling of the active sites by metals and is limited to operating temperatures less than 50° C.

Other examples of solid super catalysts are shown in Saha et. al., “A New Method for the Preparation of Peroxyacetic Acid Using Solid Superacid Catalysts,” where both a reactor and continuous flow reactors are described. The principal solid super acids include sulfonated styrenes and sulfonated tetrafluoroethylenes. The production rate of peracetic is too slow to be of commercial importance and to meet the demands of typical applications.

There remains a need for small, modular, and cost effective method for producing and applying PAA into various applications while producing minimal waste products. It would be especially desirable to develop a continuous process capable of producing PAA in an aqueous medium on-site and with variable on-demand controls to treat a wide variety of applications, especially one that can operate under a wide variety of processing conditions with minimal human intervention.

BRIEF SUMMARY

In one aspect, aqueous peracetic acid is produced on-site at variable rates to meet the demands of a downstream operation. Acetic acid, hydrogen peroxide, an acid catalyst, and water are fed into a continuous tank reactor to form a reaction medium. Vapor from the reaction medium is fed into the base of a distillation column, from which product is removed as distillate or effluent. The demand for PAA in the downstream operation is determined, and the rate of PAA production is controlled by one or more of (i) increasing or decreasing catalyst concentration by purging a portion of the reaction medium from a recirculating line to the continuous tank reactor prior to introducing fresh acetic acid, hydrogen peroxide, catalyst, and water; (ii) increasing or decreasing thermal energy input into the continuous tank reactor; (iii) increasing or decreasing pressure in the continuous tank reactor to prevent the formation of a vapor phase; and (iv) changing the temperature in the continuous tank reactor.

By controlling the rate of PAA production, the volumes of reaction mixture and final product storage can be reduced. Since the volumes are kept to minimum levels before using in the intended applications, the entire process is inherently safer than alternative methods requiring handling and storage (and sometimes transportation) of large volumes of peracids prior to use.

Another aspect of the invention is directed to the in situ production of a superacid reaction intermediate, such as peroxymonosulfuric acid (Caro's Acid), to accelerate the formation of PAA. The superacid reaction intermediate can be produced by the reaction of hydrogen peroxide and the acid catalyst at higher concentrations. Prior to the addition of make-up acetic acid and/or water to the other reaction components, recycled acid catalyst stream can be mixed with some or all of the hydrogen peroxide. When the superacid reaction intermediate is contacted with the acetic acid substrate, the peroxide functionality is rapidly transferred from the intermediate to acetic acid, thereby forming peracetic acid. The process can employ a continuous tank reactor or another type of reactor, such as a tubular reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features, and wherein:

FIG. 1 is process flow diagram for the production of aqueous peracetic acid using a continuous modular apparatus employing a tubular reactor;

FIG. 2 is process flow diagram for the production of aqueous peracetic acid using a continuous modular apparatus employing a continuous tank reactor; and

FIG. 3 schematically illustrates a variety of potential end uses of aqueous peracetic acid produced on-site and on-demand.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, reference is made to the accompanying drawings, which by way of illustration show various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.

Persons experienced with the manufacture, storage, and handling of PAA are aware of safety and hazard risk assessments. Safety can be increased by minimizing the amount of reaction medium, minimizing the amount of head space above the reaction medium, minimizing the storage requirements of the finished product, and generating a minimum volume of PAA on demand only as needed. Other safety factors are enhanced by fail-safe measures in the controls where the process automatically shuts down when any of the control sensors indicate conditions outside the normal pre-set operating ranges.

The term “continuous tank reactor,” as used herein, refers to a homogeneous reactor where PAA is produced continuously at a predetermined rate and where the rate is varied by changing the mixture composition, temperature, and pressure proportional to the applications demands. The reactor is also sometimes referred to as a continuous pot reactor.

In applications where the amount of product demand exceeds the capacity of a single production unit, either a scaled-up process unit or multiple production units can be operated in parallel to meet the demand. Multiple reactors (e.g., separately or in parallel) can be used so that the output of the reactors is subsequently combined, in liquid and/or vapor form, prior to the vacuum distillation and rectification stages of the process. The effect of utilizing multiple reactors is two-fold: 1) the composite volume of potentially hazardous in-process mixtures is distributed and isolated within separate (smaller) reactors, thereby reducing the risks of rapid peroxygen decomposition and minimizing the impact should such an event occur; and 2) individual reactors may be turned on or off with the effect of isolating and/or remedying a developing hazard in one of the reactors, and/or varying the immediate output, such as the case where the rate of peracetic acid product produced from the process is integrally linked to the demand of a proximate end-use application. In the case where multiple reactors are of tubular design, the number and size of the reactors may be such to encompass microchannel reactors, the interior walls of which are coated with a substance containing moieties related to one or more of the following: sulfuric acid, sulfonic acid, phosphotungstic acid, phosphomolybdic acid, phosphoric acid, phosphonic acid, silicic acid, and zirconium phosphate. The consumable reactants and catalyst(s) can be premixed in a common chamber prior to being distributed to the individual reactors.

The PAA vapor (or a water vapor azeotrope) can be fed into an application stream by passing each into a suitable inductor, such as a conventional venturi contactor, where the stream and PAA vapor are mixed together. Alternatively, PAA vapor may be applied directly as a gas into the application without inducting or condensing into an aqueous solution.

The rate of production of PAA can be modulated by an electronic controller, for example, a process logic controller (PLC), where signals from the end-use application are used to evaluate and control the reaction and distillation processes to produce the required amount of PAA on-demand.

The processes described herein are useful in connection with a variety of downstream operations. Of particular commercial importance are the treatment and disinfection of municipal sewage wastewater treatment plant discharges. The production equipment can be sized according to the demand of the downstream operation and preferably is capable of variable production to match low and high daily demand variances. The present invention is useful for the production of PAA for the treatment of a wide variety of water, wastewater, industrial streams, commercial articles, and in the manufacture or purification of chemical compounds and intermediates. Non-limiting examples of other downstream operations include industrial wastewaters, petroleum desulfurization, cooling water circuits, de-inking, cellulose pulp and paper bleaching, textile bleaching, institutional laundries, potable water, process water, recreational and agricultural water, and food and beverage equipment (depicted in FIG. 3). Non-limiting examples of chemical compounds and intermediates manufacture includes the epoxidation and hydroxylation of natural oils used in the plastics, paint and coatings industries, as well as the epoxidation of other natural or synthetic olefins. Other non-limiting examples include the fumigation of e.g., buildings, structures, grains, soils, fruits, vegetables, animals or other articles of commercial value.

In general, the present invention has utility for the treatment of any stream susceptible to treatment by PAA or transformation of a compound by PAA. A “stream susceptible to treatment by PAA” refers to any water, wastewater, or industrial stream for which PAA, with or without additional treatments, would reduce the population of microorganisms (non-limiting examples like protozoa, bacteria, pathogens and viruses) and/or render the stream less toxic, less sulfurous, or otherwise more suitable for or compatible with downstream distribution systems or discharge to a receiving watershed. A “transformation of a compound” refers to any chemical compound that is capable of reacting with PAA to form a new (or purer) chemical species, such as an intermediate or finished product.

Aqueous peracetic acid can be produced from the acid catalyzed reaction between acetic acid (HOAc), and hydrogen peroxide in water in a suitable reaction vessel, distilled off, and applied as either a condensed aqueous solution or as a vapor finished product. The finished product is fed proportionally and directly into the end-use applications as it is produced. The initial phase of the process involves continuously adding the reactants in specific ratios together to produce PAA (also represented as HOOAc) at any concentration, up to and including a steady-state concentration. The rate of PAA formation is proportional to the concentration of acid catalyst, the concentration of each reactant, the temperature of the reaction, and the temperature and pressure of distillation. The overall process chemistry, with sulfuric acid shown as an exemplary acid catalyst, is expressed in Table 1: TABLE 1

where, a,b,c,e,f,g,h,i = molar or % weight ratios xs = excess amount eq Rxn = equilibrium reaction (reversible)

While sulfuric acid is described as an exemplary acid catalyst, a variety of other acid catalysts can be used, non-limiting examples of which include strong mineral acids, such as phosphoric acids, such as phosphoric acid, orthophosphoric acid, monohydrogen-phosphoric acid, dihydrogenphosphoric acid, or the respective phosphate salt analogues thereof; sulfonic acids, such as sulfonic acid or an organosulfonic acid of formula R—S(═O)₂OH where R is an organic or organosulfonate analogue of formula R—S(═O)₂O⁻X⁺ where X⁺ is the conjugate salt ion; phosphotungstic acids, such as phosphotungstic acid, tungstophosphoric acid, or tungsten hydrogen oxide phosphate; phosphomolybdic acids, such as phosphomolybdic acid or an analogue salt thereof; phosphonic acids, such as those of formula R₁P(═O)OR₂OR₃ where R₁, R₂, and R₃ represent organic molecules, or an analogue salt thereof; silicic acids, such as of formula SiO_(x)(OH)_(4-2x) (e.g., where x is 1-2); metasilicic acid (H₂SiO₃), orthosilicic acid (H₄SiO₄), disilicic acid (H₂Si₂O₅), and pyrosilicic acid (H₆Si₂O₇); zirconium phosphates; sulfated zirconias; sulfonated polystyrenes, such as a sulfonated polystyrene divinylbenzene copolymer; and sulfonated tetrafluoroethylene ethers, such as a tetrafluoroethyleneperfluoro [2-(fluorosulfonylethoxy)propyl]vinylether polymer.

Another aspect of the invention is directed to the in situ production of a superacid reaction intermediate, such as peroxymonosulfuric acid (Caro's Acid), to accelerate the formation of PAA. The superacid reaction intermediate can be produced by the reaction of hydrogen peroxide and the acid catalyst at higher concentrations. Prior to the addition of make-up acetic acid and/or water to the other reaction components, recycled acid catalyst stream can be mixed with some or all of the hydrogen peroxide. When the superacid reaction intermediate is contacted with the acetic acid substrate, the peroxide functionality is rapidly transferred from the intermediate to acetic acid, thereby forming peracetic acid. The effect of this sequence is two-fold: 1) the overall rate of peracetic acid formation is increased, which allows the volume of in-process liquids to be reduced; and 2) potentially explosive mixtures which may form within a peracetic acid production process are minimized, e.g., the acetic acid is largely isolated from hydrogen peroxide. The superacid reaction intermediate can be affixed to a solid support or tubular reactor wall, which is contacted sequentially and repeatedly with hydrogen peroxide then acetic acid. This way, the effluent from the hydrogen peroxide sequence may be discarded from the process, added to the proximate end-use application for the distilled peracetic acid product, and/or re-introduced into the peracetic acid production process e.g., via pre-mixing into the hydrogen peroxide feed.

An acid catalyst-containing purge stream can be taken from the continuous tank reactor (or the base of the distillation column in the case of the tubular reactor) and used to manufacture another (e.g., less volatile) peracid, e.g., a higher molecular weight peroxycarboxylic acid such as peroctanoic acid and/or peroxymonosulfuric acid. Depending on the particular composition of the purge stream, additional hydrogen peroxide and/or acid catalyst can be added to form a desired peracid(s). The other peracid can be used for something other than a peroxide transfer agent for peracetic acid formation. Both processes (the production of distilled peracetic acid and the production of another peracid produced from the purge stream) can be integrated and the two product streams added concurrently to an end-use application, either as separate solutions or as a single (combined) solution. The effect of such a mixed peracid production process can be to provide improved end-use performance relative to either peracid alone. Non-limiting examples of end-use applications include disinfection, bleaching, delignification, desulfurization, and general oxidation.

The stoichiometry of the reaction predicts that 1 mole of acetic acid requires 1 mole of hydrogen peroxide to produce 1 mole of PAA when the reaction is 100% efficient. Since the PAA is in equilibrium with the reactants, then less than stoichiometric amounts of PAA are produced in the reactor. The molar ratios of reactants and yields of eq-PAA are depicted in Table 2 with respect to acetic acid concentration at unity. TABLE 2 Molar Ratios and Yields of PAA at Equilibrium With Respect to HOAc at Unity (In 0.7% w/w catalyst) HOAc, mole H₂O₂, mole PAA, mole 1.00 0.41 0.29 1.00 0.50 0.32 1.00 1.00 0.44 1.00 1.65 0.52

The molar ratios of reactants and yields of eq-PAA are depicted in Table 3 with respect to hydrogen peroxide concentration at unity. TABLE 3 Molar Ratios and Yields of PAA at Equilibrium With Respect to H₂O₂ at Unity (0.7% catalyst) HOAc, mole H₂O₂, mole PAA, mole 0.61 1.00 0.32 1.00 1.00 0.44 2.00 1.00 0.66 2.40 1.00 0.70

Since PAA is distilled off at a variable rate, equilibrium conditions are never met and the reaction shifts or pushes to the right (Table 1). The reactant concentrations or molar ratios may be increased to produce PAA at an increased yield, or reduced to lower the yield. The reactants concentrations are varied according to the rate of production required to meet the application demand.

The reaction between only acetic acid and hydrogen peroxide in water proceeds to equilibrium, although the rate is too slow to be of practical commercial use. Fundamental laws of chemistry also demonstrate that the rates are proportional to the concentration of the primary reactants. However, even at high concentrations, the rate is too slow for practical use.

To increase the rate of PAA formation, an acid catalyst is added. Any of the above-described acid catalysts can be used. When the acid catalyst concentration is sufficiently high, it is thought that it participates as a reversible superacid (for example Caro's Acid, peroxymonosulfuric acid) or other intermediate since the rate varies with the amount of sulfuric acid and hydrogen peroxide added in the reaction. The rate of PAA formation increases with the concentration of sulfuric acid, as depicted in Table 4. Acid concentrations above 30% are difficult to maintain since the concentrations are limited to the dilution effects from the other reactants. The rates shown illustrate the effect of an exemplary sulfuric acid catalyst. TABLE 4 Initial Rates of PAA Formation Initial Rate of Catalyst PAA Formation HOAc, mole H₂O₂, mole % H₂SO₄ mole/min 1.00 1.00 0.00 <0.0001 1.00 1.00 0.70 0.07 1.00 1.00 10.0 0.17 1.00 1.00 20.0 0.26 1.00 1.00 30.0 0.31

The rate of formation of PAA can be controlled, for example, by varying the amount of acid catalyst during the reaction. Once the reaction is initiated, the rate may be increased by adding either fresh or recycled catalyst. To decrease the rate, reactive mixture containing catalyst can be removed to a recycle drum where it is re-used to increase the rate. Excess catalyst can be removed through a blowdown line and fed into the receiving application, thus eliminating any accumulation of waste products. Impurities collected in the reaction mixture, for example heavy metals leached from the materials of construction and from the reactants, also can be removed in the blowdown. As the PAA is distilled off, the reaction shifts to the right of the equation (Table 1) and produces PAA at near initial rate conditions depicted in Table 4. Another catalyst of sulfated zirconia, preferably containing tungsten and/or phosphate, further accelerates the formation of PAA and may be used in a similar fashion to control the reaction rate.

The effect of temperature on the rate of the reaction follows typical Arrhenius behavior. Temperature increases alone are not sufficient to achieve yields of PAA since increasing the temperature above 65° C. accelerates the decomposition of PAA and H₂O₂, thereby limiting performance. However, increasing the temperature when sulfuric acid catalyst is present increases the yield exponentially. Therefore, adjusting the temperature, from ambient to 20-60° C. provides another method of control to preselect the production rate of PAA. The heat energy applied can be varied in proportion to the desired rate of production to meet the application demand.

The rate of production of PAA can be further controlled by the pressure and temperature during distillation. A pressure range of about 25 to 200 torr (3 to 27 KPa) is preferred, especially from 50 to 100 torr (7 to 13 KPa), within temperature range of 20 to 65° C. in the distillation column. Therefore, adjusting the pressure and temperature during distillation provides another method of control to preselect the rate of PAA produced. The vacuum and temperature applied can be varied in proportion to the desired rate of production required to meet the application demand.

Aqueous PAA can be produced using a tubular reactor, as illustrated in FIG. 1, or a continuous tank reactor, as illustrated in FIG. 2. In the tubular reactor depicted in FIG. 1, hydrogen peroxide, acetic acid, sulfuric acid catalyst and water (which are typically added entirely with the hydrogen peroxide and/or acetic acid) are fed to the reactor together with recirculated reaction mixture from the base of the distillation column. Heat for the reaction can be provided by a jacket on the tubular reactor, which is operated under sufficient pressure (e.g., controlled by a back-pressure control valve in the reactor discharge line) to prevent vaporization within the reactor. When the reaction mixture discharges from the reactor into the base of the distillation column, which operates at a lower temperature and pressure, flashing takes place. The vapor rises through the distillation column, where it is rectified to give the desired PAA concentration with minimal levels of residual hydrogen peroxide and acetic acid. The liquid recirculates to the tubular reactor. The operation of the reactor and associated equipment is modulated to produce sufficient PAA to meet the demands of each application.

In the continuous tank reactor depicted in FIG. 2, the reactants are typically charged at the base of the distillation column, and distillation takes place as a result of heat added by a jacket on the reactor using hot water or other heating medium. Reflux is returned to the column to give the desired rectification, while the balance of the vapor is condensed and fed to the application or it is fed directly to the application as a vapor.

Tubular Reactor

FIG. 1 illustrates a tubular reactor [11], which is particularly well-suited for larger scale operations, though it may be employed for any scale of operation. The raw materials, including acetic acid [1], hydrogen peroxide [2], sulfuric acid [3], and deionized water [4], which is usually or primarily charged with acetic acid and hydrogen peroxide, are charged to the tubular reactor [11], which is jacketed [10] and preceded by an in-line mixer [9]. The raw materials are charged at a rate corresponding to the desired production rate. The tubular reactor [11] operates at higher temperatures than have heretofore been employed in the production of aqueous peracetic acid and at pressures sufficient to prevent vaporization within the reactor. When the reaction mixture exits the reactor [11] through a back-pressure valve [12], it discharges into the base of the distillation column [5], where it flashes at the lower pressure within the column. The vapor rises through the column [14], where it is rectified to give the desired distillate concentration. The constant composition reaction mixture in the base of the column [5] after flashing is re-circulated to the reactor [11] where it is combined with fresh reactants. To increase production, the feed rates of all reactants are increased proportionately. Some reduction in purge rate from the base of the column may be needed to increase the catalyst concentration in the reaction mixture to achieve increased production rates and/or the temperature may need to be increased. The residence time in the reactor [11] typically ranges from 1 to 30 minutes, preferably 1 to 10 minutes. The reaction temperature within the reactor [11] will typically be in the range of 60-80° C. and the pressure will typically be in the range of 500-1500 mm Hg abs.

Continuous Tank Reactor

In the embodiment illustrated in FIG. 2, precursors including acetic acid [1], hydrogen peroxide [2], acid catalyst such as sulfuric acid [3], and deionized water [4], which is usually added with the hydrogen peroxide and/or acetic acid, are fed into the base [5] of the distillation column, which functions as the continuous tank reactor. Vacuum can be applied at the desired level and the reaction medium can be heated to a suitable reaction temperature. The feeding of hydrogen peroxide, acetic acid and sulfuric acid (usually premixed with the acetic acid) are then started. Heat can be applied to the reactor by low pressure steam or hot water circulated through a jacket, or by an electric heater to achieve the desired constant rate of vaporization which will maintain the level in the pot while simultaneously removing a small liquid purge stream or blowdown from the pot.

Distillation Column

With reference to FIGS. 1 and 2, the top of the distillation column [14] can be connected to a condenser [15] where the vapor from the top of the column is condensed. The distillation column [14] may contain one or more theoretical plates. The column may contain as many as 10 or more theoretical plates but in practice usually contains about 3-6 theoretical plates. A portion of the condensate is returned to the top of the column to provide the reflux [17] needed for the rectification of the vapor, while the balance of the distillate is transferred from the distillate receiver [16] to a day drum [18]. The vacuum in the system is provided by a vacuum pump [20] such as a liquid-ring pump using water as a seal liquid. A typical analysis of the distillate is 25% peracetic acid, less than 1% hydrogen peroxide, less than 4% acetic acid, and the balance water. The boiling vapor mixture from the base of the distillation column [5] passes into the bottom of the column [14] at temperatures often in the range of 40-60° C., more typically in the range of 45-55° C., and at pressures often in the range of 30-200 torr, typically in the range of 50-100 torr.

Optionally, a portion of the vapor from the top of the column [14] may be used without condensation by being educted into a water or air vapor stream to be treated, where the eductor system provides the required vacuum, or it may be withdrawn through a dry vacuum pump; with the balance of the vapor from the top of the column being condensed to provide the reflux needed and a small amount of additional liquid peracetic acid solution that is accumulated in the day drum [18] for use as a liquid and during startup of the system.

Recycle Drum

To reduce the rate of the reaction, some of the reacting media can be moved to a recycle drum [6] where the sulfuric acid concentration is thereby reduced in the reactor. When it is desired to increase the rate, the catalyst stored in recycle drum [6] can be introduced back into the reactor. Fresh acid catalyst may also be added into the reactor to make up for losses elsewhere.

Blowdown

Periodically, a reactor blowdown stream is removed from the reactor to prevent the buildup of contaminants in the reactor and remove excess catalyst. The blowdown can be added directly to the receiving application [7], a non-limiting example includes directing the blowdown into a wastewater treatment plant stream, to prevent accumulating and disposing of waste products. The volume of blowdown typically is relatively small and the impact in the receiving application is often negligible.

Temperature

The reaction mixture can be heated by a suitable source and continuously mixed by a suitable stirrer or boiling action. The mixture can be boiled under low pressure using a suitable vacuum pump [20]. The boiling mixture vapor passes into the distillation column [14] where the components are separated into PAA and water at the rate of PAA desired. The distillation column may contain a suitable packing, such as ceramic or polymeric packing.

Vacuum System and Vent

Vacuum can be provided by a liquid-ring vacuum pump [20] using water on a once-through basis as the seal liquid. If the end use of the PAA is for wastewater treatment, that water may be used as the seal liquid. All condensibles remaining in the vent from the condenser can be absorbed in the water used as the seal liquid. The level of vacuum is controlled by admitting air to the inlet of the vacuum pump. The vent from the vacuum pump, which typically is substantially free of organic contaminants, is discharged to the atmosphere.

Alternatively, for some applications such as wastewater treatment, the vacuum may be provided by an eductor system [22] using the water to be treated as the motive fluid. Here too the air in the flow to the eductor system will either dissolve in the water to be treated or it will separate from the water substantially free of any organic contaminants. Alternatively, a dry vacuum pump [25] may be used where the vapor is to be used for gas phase applications [26], for example to disinfect soil, fruits or vegetables.

Condenser

A condenser [15] using chilled water as a coolant can be used to condense all or a portion of the vapor from the top of the column [14]. The condensate drains into the distillate receiver [16], from which part of it is pumped to the top of the column as reflux [17] and the balance is pumped to the day drum [18], from which it is pumped to the end-use application as needed or accumulated for supplementary uses and startup following a shutdown.

Vaporous PAA

Vaporous PAA can be added directly into an end-use application stream. For example, an application stream [24] can be circulated through a contactor [22], such as a venturi inductor, where the PAA vapor dissolves directly into the stream. Alternatively, direct contact between gaseous PAA and the application [26] can be accomplished, for example, by a gas phase reaction between vapor PAA and solid substrates such as grains, fruits and vegetables [72], and soils [75].

Controller

The process and applications can be managed by a computerized controller [27] where input/output (I/O) channels [13], [28], [29], [30], and [31], shown in FIGS. 1, 2, and 3, send and receive information to the process modules. The process modules may include the chemical precursors and reactors, distillation equipment and PAA products, and applications. The controller comprises a computer or PLC and human machine interface (HMI) [27] where the operation of the entire process is maintained. The production of PAA can be modulated to a desired rate within the design specifications of each process model.

End-Use Applications

Aqueous peracetic acid can be produced at a rate appropriate for subsequent end use applications, such as [50] through [77] depicted in FIG. 3. Of particular commercial importance is the treatment and disinfection of municipal sewage wastewater treatment plant (WWTP) discharges. The present invention is also useful for the production of PAA and treatment of a wide variety of water, wastewater, industrial effluents, food and beverage, and in the manufacture of chemical compounds and intermediates. Non-limiting examples of end use applications are discussed by way of examples for each of the following industries:

-   -   Municipal Wastewater Treatment [50]         -   Municipal Wastewater Disinfection         -   Combined Sewer Overflow Disinfection     -   Industrial [53]         -   Industrial Wastewater Treatment         -   Petroleum Desulfurization     -   Cooling Water Treatment [56]     -   Bleaching [59]         -   De-Inking         -   Pulp and Paper Bleaching         -   Textiles Bleaching         -   Institutional Laundries Bleaching     -   Water Treatment [62]         -   Potable Water Disinfection         -   Process Water Sanitizing     -   Food And Beverage Equipment Sanitizing [66]     -   Chemical Processing [69]

Applications using PAA traditionally use equilibrium PAA where significant amounts of the reactants (namely H₂O₂, HOAc, and sulfuric acid) remain in the equilibrium product. The applications listed above generally operate at a much lower cost using PAA compared to eq-PAA since all precursor chemicals are reacted into PAA, while the sulfuric acid catalyst is purged from the reactor. Operating costs are lowered further where the precursor chemicals are delivered to the customer in bulk packaging, for example in truckload quantities, where PAA is produced on-site at bulk chemical prices. By comparison, currently PAA must be delivered in packaged quantities less than 300 gallons, which greatly increases the chemical prices, handling requirements, and operating costs.

Municipal Wastewater Disinfection [50] (cf. Disinfection Basin [51])

The largest application of PAA is for the disinfection of municipal wastewater effluents [50], e.g., as an alternative to chlorine based disinfection. PAA can be applied to the wastewater final stage at a concentration usually ranging from about 0.5 to 25 mg/L, more preferably from about 5 to 15 mg/L, to achieve disinfection standards for discharge to a receiving watershed. In older construction specifications, the aqueous PAA may be applied directly into an existing disinfection basin [51] with no additional capital improvements, a non-limiting example is a typical basin exhibiting plug flow characteristics previously used for conventional chlorine based disinfection processes. Although the size of the basin originally used for chlorine disinfection is based on a minimum 30 min. contact time, the time required for aqueous PAA disinfection is in the order of 5 to 7 min. The extra capacity of an existing disinfection basin does not limit the performance of aqueous PAA. In new construction specifications, a disinfection basin employing aqueous PAA requires a much smaller footprint, less volume, and less retention time compared to traditional chlorination. Hence, the capital and operating cost are further reduced using aqueous PAA disinfection.

Environmental regulations and discharge permits promulgated in the Clean Water Act of 1972 and later amendments, restrict chlorine residuals in wastewater discharges to a receiving watershed. To meet these guidelines, dechlorination is required to eliminate the residual chlorine. Typical dechlorination processes add gaseous sulfur dioxide or sodium bisulfite solutions into a dechlorination basin prior to discharge. Disinfection basins have been modified and constructed to include both chlorination and dechlorination chambers. The use of aqueous PAA disinfection does not require any additional treatment prior to discharge. Any residual aqueous PAA will transform to acetic acid, water, and oxygen with no significant impact on any discharge parameters, non-limiting examples of discharge parameters include TOC, COD, BOD, and toxicity.

A disinfection basin [51] using (but not limited to) a typical oxidation basin design is well suited for aqueous PAA applications. The disinfection can be monitored and controlled by a PLC and electronic sensors located throughout the disinfection process, non-limiting controls include Oxidation-Reduction Potential (ORP) and Ion Selective Probes (ISP). The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA can be modulated to meet the demands. Depending on the extent of automation at the site of use, the user's controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Combined Sever Overflow [50] (cf. Disinfection Chamber [51])

Throughout the modern world, municipal wastewater treatment plants (WWTPs) have the authority to bypass incoming sewage during times of high storm activity and flooding to protect the facility from hydraulic washout, termed Combined Sewer Overflow (CSO). During a bypass event, discharge permit limits and reportable quantities may be exceeded, including no disinfection, without violation or penalty. However, new regulations promulgated by Federal agencies prohibit the discharge of CSO without disinfection. As a disinfection agent, aqueous PAA is also cost effective compared to conventional chlorination and dechlorination practices, including but not limited to, sodium hypochlorite (termed “hypochlorite”) and sodium bisulfite (termed “bisulfite”) processes, respectively.

Hypochlorite based disinfection programs require large chemical storage tanks and large disinfection chambers to meet the treatment requirements during a CSO event. During a long period between CSO events, for example greater than three months, the stored hypochlorite will loose significant amounts of active available chlorine. The half-life of hypochlorite can be less than one year which suggests longer storage periods will not have adequate amounts of active chlorine available during a CSO event. Tanks with high capacities must be installed as a contingency and poses further safety concerns and hazard risk profiles. The size of the chlorination and dechlorination disinfection chambers will depend on the CSO incursion rate expected and the minimum 30 min. contact time required.

The advantage of the present invention over existing technologies is aqueous PAA is produced on-site and available at full strength and on-demand regardless of the storage or shelf life of the precursor chemicals. For example, only H₂O₂ may be considered to have a limiting shelf life, however, <1% degradation per year is expected and any losses will have no impact on the production or use of aqueous PAA when needed.

A typical disinfection basin [51] using (but not limited to) a typical oxidation ditch design is well suited for aqueous PAA applications. The disinfection is monitored and controlled by a PLC and electronic sensors located throughout the disinfection process, non-limiting controls include ORP and ISP. The performance of the application is evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Industrial Wastewater [53] (cf. Plug Flow Reactor [54])

Many types of industrial wastewaters [53] are not amenable to disposal in conventional biological wastewater treatment plants due to high loading characteristics, for example TOC, COD, and BOD, and toxic properties, for example refractory and phenolic compounds. Pretreatment applications include chemical oxidation to destroy the precursors responsible for toxicity and to transform refractory compounds into products easily assimilated in the biological treatment process [55]. In cases where a selective chemical oxidizer is required, aqueous PAA oxidizes substrates that are not otherwise oxidized by other oxidation programs. Aqueous PAA is most efficient when used in concentration ranges from about 10 to 250 mg/L for typical applications and up to about 100 to 10,000 mg/L for highly refractory compounds.

A plug flow reactor design [54] comprising a given length of pipe, or similar conduit, but not limited to, is well suited to pretreat industrial wastewaters. The industrial wastewater process is monitored and controlled by a PLC and electronic sensors located throughout the industrial wastewater treatment process, non-limiting controls include ORP, ISP, pH, and automatic titrators. The performance of the application is evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Petroleum Desulfurization [53] (cf. Plug Flow Reactor [54])

Worldwide guidelines requiring low sulfur content fuels has promoted the application of aqueous PAA for the oxidation and removal of sulfur compounds such as sulfides, mercaptans, thiophenes, and similar analogues. Petroleum desulfurization by oxidation of sulfides and thiols (mercaptans) can use aqueous PAA at concentrations ranging from 1 to 5,000 mg/L, typically 50 to 500 mg/L, in finished gasoline, kerosene, and diesel fuels, without limitation.

A plug flow reactor design [54] comprising a given length of pipe, or similar conduit, but not limited to, is well suited to pretreat petroleum products. The desulfurization process can be monitored and controlled by a PLC and electronic sensors located throughout the desulfurization process, non-limiting controls include ISP's and automatic inline sulfur analyzers. The performance of the application is evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Cooling Water [56] (cf. Cooling Water Circuit [57])

Cooling water circuits [56] used throughout manufacturing, industrial, and electrical generation plants suffer greatly from the effects of biological growth and microorganisms. Aqueous PAA can be effective for controlling biological growth and limiting the deleterious effects caused in cooling water circuits. Aqueous PAA is effective, for example, at concentrations from 0.5 to 100 mg/L, typically from 2 to 25 mg/L, in most applications. Aqueous PAA may be applied directly to the cooling water circuit without any capital improvements to existing facilities.

The cooling water quality can be monitored and controlled by a PLC and electronic sensors located throughout the cooling water circuit, non-limiting controls include ORP and ISP. The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

De-Inking [59] (cf. Bleaching Equipment [60])

The recycling of paper products requires that the resulting pulp be free of the colors contained in the original material. Aqueous PAA is particularly effective for the de-inking [53] of these products. Aqueous PAA is effective, for example, at concentrations from 1 to 5,000 mg/L, typically from 100 to 1,000 mg/L, in most applications. Aqueous PAA may be applied directly to the deinking processes with little or no capital improvements to existing facilities.

The deinking process can be monitored by a PLC and electronic sensors located throughout the deinking process, non-limiting controls include ORP, ISP, and brightness measurements. The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Pulp And Paper Bleaching And Delignification [59] (Bleaching Equipment [60])

The bleaching and delignification of cellulose pulp [59] typically yields better results using aqueous PAA compared to conventional chlorine or hydrogen peroxide based processes. Aqueous PAA is effective, for example, from 100 to 1,000 mg/L and up to 1 to 5% concentrations, depending on the application. Aqueous PAA may be applied directly to the manufacturing circuit in conventional bleaching baths without extensive capital improvements to existing facilities.

The bleaching and delignification processes can be monitored and controlled by a PLC and electronic sensors located throughout the bleaching and delignification processes, non-limiting controls include ORP, ISP, automatic titrators, and brightness measurements. The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Textiles [59] (cf. Bleaching Equipment [60])

The bleaching of textiles [59] demonstrates better properties using aqueous PAA compared to conventional chlorine or hydrogen peroxide based processes. Aqueous PAA is effective, for example, from about 100 to 1,000 mg/L and up to about 1 to 5% concentrations, depending on the application. Aqueous PAA may be applied directly to the manufacturing circuit in conventional equipment without extensive capital improvements to existing facilities.

The textile processes can be monitored and controlled by a PLC and electronic sensors located throughout the textile processes, non-limiting controls include ORP, ISP, automatic titrators, and brightness measurements. The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Institutional Laundries [59] (cf. Bleaching Equipment [60])

The color safe bleaching of clothing and other fabrics in institutional laundries

demonstrates better properties using aqueous PAA compared to conventional chlorine or peroxide based processes. Aqueous PAA is effective, for example, from about 50 to 10,000 mg/L, typically from about 100 to 500 mg/L, depending on the items being laundered.

The laundry process can be monitored and controlled by a PLC and electronic sensors located throughout the process, non-limiting controls include ORP, ISP, and brightness measurements. The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA can be modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Potable Water Treatment [62] (cf. Reactor And Clarifier [63])

There is considerable momentum, partially from the U.S. Environmental Protection Agency (EPA), to promote total free chlorine (TFC) disinfection programs in potable water [62]. Aqueous PAA can be effective for disinfection during contact treatment [63], and equally important, as a post treatment disinfectant throughout the distribution system to the point-of-use (POU) [64], or at the “tap.” Aqueous PAA is effective, for example, at concentrations from about 0.5 to 5 mg/L during contact treatment and positive residuals of about 0.25 to 2 mg/L in the distribution network. Aqueous PAA may be applied directly to existing water intake, storage, treatment and distribution systems without extensive capital improvements. The sludge produced [65] may also be disinfected.

The potable water process can be monitored and controlled by a PLC and electronic sensors located throughout the process [63], non-limiting controls include ORP, pH, and ISP measurements. The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands.

Potable Water Distribution Network [64]

Following the treatment of potable water, the residual aqueous PAA in the distribution network and piping can be monitored and controlled by a PLC and electronic sensors, non-limiting controls include ORP, pH, and ISP measurements. Data from the distribution network can be transmitted back to the PLC where the performance of the distribution system can be evaluated and the production and quality of aqueous PAA modulated to meet the demands. Depending on the extent of automation at the site of use, the user's controllers may be interfaced with the aqueous PAA process PLC without redundant controls and sensors.

Process Water Treatment [62] (cf. Reactor And Clarifier [63])

Process waters [62] obtained from surface impoundments, for example rivers and lakes, pose a particular problem to the facility operations due to colloidal suspensions, microorganisms, and plant matter. The oxidation and disinfection properties of aqueous PAA make it particularly useful in achieving a clarified product with minimal additional water treatment additives. Depending on the initial quality of the water, aqueous PAA is effective from about 0.5 to 50 mg/L, often from about 5 to 25 mg/L. Aqueous PAA may be applied directly to existing process water circuits without extensive capital improvements.

The quality of process water can be monitored and controlled by a PLC and electronic sensors located throughout the process, non-limiting controls include ORP, pH, and ISP. The performance of the application can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Foods Beverage and Fermentation Equipment Sanitation [66] (cf. Food and Beverage Equipment [67])

Chlorine based sanitizing programs have been traditionally employed in the food, beverage and fermentation industries [66], non-limiting examples include food processing plants, fruits and vegetables conveyance, and processing vats including alcoholic beverages, soft drink production and chemicals produced by fermentation [67]. Eq-PAA was introduced as an effective alternative, however, it is known that the active sanitizing ingredient in eq-PAA is the PAA. Production of aqueous PAA on-site and on-demand is more cost effective and safer to handle than conventional eq-PAA. Depending on the initial contamination of the equipment, aqueous PAA is effective, for example, from about 0.5 to 1,000 mg/L, more preferably 100 to 250 mg/L. Aqueous PAA may be applied directly to existing equipment without extensive capital improvements.

Sanitizing processes can be monitored and controlled by a PLC and electronic sensors located throughout the process [67], non-limiting controls include ORP and ISP measurements. The performance of the application [68] can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Chemical Processing [69] (cf. Chemical Reactors [70])

Chemical compounds and intermediates manufacture [69] includes, but is not limited to, the use of aqueous PAA for oxidations such as epoxidation and hydroxylation of olefinic materials such as natural oils, hydrocarbons, etc. Traditionally, these epoxides and other oxidation products are used as is or as reactive intermediates in the paint and coatings, adhesives, plastic additives, lube and fuel additives, personal care, and oil field processing industries. The epoxidation and hydroxylation of olefinic compounds historically uses eq-PAA, where the remaining H₂O₂, HOAc and sulfuric acid are not utilized and therefore wasted, or it is performed using the on-site production of the PAA from these reactants. But, in using epoxidation chemistry it is very difficult to stop the formation of by-products that result from the reaction of the sulfuric acid and even the acetic acid with the epoxidation or oxidation product. Aqueous PAA can be produced where all of the reactants are transformed into aqueous PAA with no significant reactants lost or wasted. Thus, PAA can be produced at substantially less cost per active unit compared to eq-PAA. The availability of aqueous PAA produced may be used in various chemical processing [69] of products synthesized only from aqueous PAA [71]. As will be appreciated by persons skilled in the art, the reaction stoichiometry and particulars of the reaction equipment [70] will dependent on such factors as the type of synthesis and product specifications.

The chemical manufacturing processes can be monitored by a PLC including I/O channels from the manufacturing equipment. The performance of the application [71] can be evaluated by the PLC and the production and quality of aqueous PAA is modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

Grain Sterilization [72] (cf. Grain Sterilization [73])

Vaporous PAA may be used for grain sterilization [72] as an alternative to present gaseous methyl bromide sterilization technology. The aqueous PAA can be applied directly as a gaseous product [26], non-limiting examples include to grain silos or other stowage [73].

The performance of the application [74] can be evaluated by the PLC and the production and quality of aqueous PAA can be modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce control redundant controls and sensors.

Soil Sterilization [75] (cf. Soil Sterilization [76])

The application of vapor PAA for soil sterilization [75] can be used as an alternative to other soil sterilization technologies. The aqueous PAA can be applied as a gaseous product [26] directly into soil strata [76]. In some applications, aqueous PAA may be applied also as an aqueous solution [75].

The performance of the application [77] can be evaluated by the PLC and the production and quality of aqueous PAA can be modulated to meet the demands. Depending on the extent of automation at the site of use, the user's existing controller may be interfaced with the aqueous PAA process PLC to reduce redundant controls and sensors.

While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims. 

1. A continuous process for producing peracetic acid on-site and on-demand at a controlled rate compatible with the demand for peracetic acid in a downstream operation, the process comprising: (a) feeding acetic acid, hydrogen peroxide, an acid catalyst, and water into a continuous tank reactor to form a reaction medium; (b) feeding vapor from the reaction medium into the base of a distillation column, from which product is removed as distillate or effluent; (c) determining the demand for peracetic acid in the downstream operation; and (d) controlling the rate of peracetic acid discharged from the distillation column so that the rate is compatible with the demand for peracetic acid in the downstream operation; wherein the rate of peracetic acid discharged from the distillation column is controlled by at least one of: (i) increasing or decreasing catalyst concentration by purging a portion of the reaction medium from a recirculating line to the continuous tank reactor prior to introducing fresh acetic acid, hydrogen peroxide, catalyst, and water; (ii) increasing or decreasing thermal energy input into the continuous tank reactor; (iii) increasing or decreasing pressure in the continuous tank reactor to prevent the formation of a vapor phase; and (iv) changing the temperature in the continuous tank reactor.
 2. The process of claim 1 wherein the effluent stream comprises peracetic acid in an aqueous solution.
 3. The process of claim 1 wherein the effluent stream comprises peracetic acid in a vapor phase.
 4. The process of claim 1 wherein the hydrogen peroxide is pre-mixed with the acid catalyst, and thereafter contacted with the acetic acid to form peracetic acid.
 5. The process of claim 1 wherein the acetic acid is pre-mixed with the acid catalyst, and thereafter contacted with the hydrogen peroxide to form peracetic acid.
 6. The process of claim 1 wherein the deionized water is pre-mixed with the acid catalyst, and thereafter contacted with the hydrogen peroxide and acetic acid to form peracetic acid.
 7. The process of claim 1 wherein a portion of the reaction medium is purged from a recirculating line prior to the introduction of fresh acetic acid, hydrogen peroxide, catalyst, and water to prevent buildup of trace metal contaminants.
 8. The process of claim 7 wherein excess acids or impurities collected in the reactor are discharged to the downstream operation.
 9. The process of claim 1 wherein vacuum in the system is created by a vacuum pump connected to the discharge end of the condenser in which the distillate is condensed.
 10. The process of claim 9 wherein the vacuum pump is a liquid-ring vacuum pump and wherein seal liquid discharge and/or the vacuum discharge from the vacuum pump is captured and fed into the downstream operation.
 11. The process of claim 1 wherein a plurality of continuous tank reactors and distillation columns are operated in parallel.
 12. The process of claim 1 wherein the molar ratio of hydrogen peroxide to acetic acid fed to the reaction system is from about 0.5:1 to about 10:1.
 13. The process of claim 12 wherein the molar ratio of hydrogen peroxide to acetic acid is from about 1:1 to about 5:1.
 14. The process of claim 13 wherein the molar ratio of hydrogen peroxide to acetic acid is from about 1:1 to about 3:1.
 15. The process of claim 1 wherein a mineral acid catalyst is premixed with acetic acid to achieve a concentration in the reactor of from about 1 to about 50 wt %.
 16. The process of claim 15 wherein the mineral acid catalyst is premixed with acetic acid to achieve a concentration in the reactor of from about 5 to 20 wt %.
 17. The process of claim 1 wherein the pressure in the distillation column is from about 3 to 27 KPa.
 18. The process of claim 17 wherein the pressure in the distillation column is from about 5 to 17 KPa.
 19. The process of claim 1 wherein the temperature in the reactor ranges from about 40 to about 100° C.
 20. The process of claim 19 wherein the temperature in the reactor ranges from about 50 to about 80° C.
 21. The process of claim 1 wherein the downstream operation is disinfection of municipal wastewater treatment plant effluent, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-wastewater effluent ratio of from about 0.5 to about 100 mg/L.
 22. The process of claim 21 wherein the peracetic acid-to-wastewater effluent ratio is from about 3 to about 25 mg/L.
 23. The process of claim 1 wherein the downstream operation is disinfection of combined sewer overflow, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-combined sewer overflow ratio of from about 0.1 to about 500 mg/L.
 24. The process of claim 23 wherein the peracetic acid-to-combined sewer overflow ratio is from about 5 to about 100 mg/L.
 25. The process of claim 1 wherein the downstream operation is reducing the concentration of undesirable organic and inorganic substances in an influent or effluent industrial wastewater stream, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-industrial wastewater ratio of from about 0.1 to about 100,000 mg/L.
 26. The process of claim 25 wherein the peracetic acid-to-industrial wastewater ratio is from about 10 to about 1,000 mg/L.
 27. The process of claim 1 wherein the downstream operation is treating petroleum products to oxidize sulfides, mercaptans, thiophenes, and similar analogues, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-petroleum products ratio of about 1 to about 5,000 mg/L.
 28. The process of claim 27 wherein the peracetic acid-to-petroleum products ratio is from about 50 to about 500 mg/L.
 29. The process of claim 1 wherein the downstream operation is disinfection of cooling waters, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-cooling water ratio of about 0.5 to 100 mg/L.
 30. The process of claim 29 wherein the peracetic acid-to-cooling water ratio is from about 2 to about 25 mg/L.
 31. The process of claim 1 wherein the downstream operation is deinking a medium containing recycled paper products, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-recycled paper products medium ratio of about 1 to about 5,000 mg/L.
 32. The process of claim 31 wherein the peracetic acid-to-recycled paper products medium ratio is from about 50 to about 1,000 mg/L.
 33. The process of claim 1 wherein the downstream operation is at least one of bleaching and delignifying a pulp or paper product stream, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-pulp or paper products stream ratio of from about 10 to about 100,000 mg/L.
 34. The process of claim 33 wherein the peracetic acid-to-pulp or paper products stream ratio is from about 100 to about 10,000 mg/L.
 35. The process of claim 1 wherein the downstream operation is bleaching a stream containing textiles, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-textile stream ratio of about 10 to about 10,000 mg/L.
 36. The process of claim 35 wherein the peracetic acid-to-textile stream ratio is from about 50 to about 1,000 mg/L.
 37. The process of claim 1 wherein the downstream operation is bleaching a stream containing institutional laundries, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-institutional laundries stream ratio of from about 50 to about 10,000 mg/L.
 38. The process of claim 37 wherein the peracetic acid-to-institutional laundries stream ratio is from about 100 to about 1,000 mg/L.
 39. The process of claim 1 wherein the downstream operation is treating and disinfecting potable water, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-potable water ratio of from about 0.5 to about 50 mg/L.
 40. The process of claim 39 wherein the peracetic acid-to-potable water ratio is from about 3 to about 50 mg/L.
 41. The process of claim 1 wherein the downstream operation is treating and disinfecting process water, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-process water ratio of from about 0.5 to about 1,000 mg/L.
 42. The process of claim 41 wherein the peracetic acid-to-process water ratio is from about 3 to about 100 mg/L.
 43. The process of claim 1 wherein the downstream operation is disinfecting and sanitizing food and beverage handling equipment, and wherein the controlled rate of peracetic acid discharge is defined by a peracetic acid-to-disinfecting and sanitizing stream ratio of from about 0.5 to about 1,000 mg/L.
 44. The process of claim 43 wherein the peracetic acid-to-disinfecting and sanitizing stream ratio is from about 3 to about 100 mg/L.
 45. The process of claim 1 wherein the downstream operation is epoxidizing and hydroxylating at least one of alkyls, oils, and fats in a chemical processing stream, and wherein the controlled rate of peracetic acid discharge is defined by a molar ratio of about 0.5:1 to about 5:1 of peracetic acid to alkyl, oils and fats.
 46. The process of claim 45 wherein the molar ratio is from about 1:1 to about 2:1 of peracetic acid to alkyl, oils and fats.
 47. A continuous process for producing peracetic acid on-site and on-demand at a controlled rate compatible with the demand for peracetic acid in a downstream operation, the process comprising: (a) preparing a superacid reaction intermediate by combining an acid catalyst and hydrogen peroxide, wherein the acid catalyst is selected from the group consisting of strong mineral acids, sulfonic acids, phosphotungstic acids, phosphomolybdic acids, phosphonic acids, silicic acids, zirconium phosphates, sulfated zirconias, sulfonated polystyrenes, and sulfonated tetrafluoroethylene ethers; (b) contacting the superacid reaction intermediate with acetic acid and water in a reactor to form a reaction medium; (c) feeding vapor from the reaction medium into the base of a distillation column, from which product is removed as distillate or effluent; and (d) controlling the rate of peracetic acid discharged from the distillation column so that the rate is compatible with the demand for peracetic acid in the downstream operation.
 48. The process of claim 47 wherein the acid catalyst is calcined into a support containing at least one of solid silica and zirconia, and wherein said support is placed into a column through which the hydrogen peroxide, a mixture of peroxyacid precursors, or both, are passed.
 49. The process of claim 47 wherein the acid catalyst comprises a strong mineral acid selected from the group consisting of sulfuric acid and a phosphoric acid.
 50. The process of claim 49 wherein the acid catalyst comprises a phosphoric acid selected from the group consisting of orthophosphoric acid, monohydrogenphosphoric acid, dihydrogenphosphoric acid, and respective phosphate salt analogues thereof.
 51. The process of claim 47 wherein the acid catalyst comprises a sulfonic acid selected from the group consisting of sulfonic acid and an organosulfonic acid of formula R—S(═O)₂OH where R is an organic or organosulfonate analogue of formula R—S(═O)₂O⁻X⁺ where X⁺ is the conjugate salt ion.
 52. The process of claim 47 wherein the acid catalyst comprises a phosphotungstic acid selected from the group consisting of phosphotungstic acid, tungstophosphoric acid, and tungsten hydrogen oxide phosphate.
 53. The process of claim 47 wherein the acid catalyst comprises a phosphomolybdic acid selected from the group consisting of phosphomolybdic acid and analogue salts thereof.
 54. The process of claim 47 wherein the acid catalyst comprises a phosphonic acid of formula R₁P(═O)OR₂OR₃, where R₁, R₂, and R₃ represent organic molecules, and analogue salts thereof.
 55. The process of claim 47 wherein the acid catalyst is selected from the group consisting of silicic acid of formula SiO_(x)(OH)_(4-2x), metasilicic acid (H₂SiO₃), orthosilicic acid (H₄SiO₄), disilicic acid (H₂Si₂O₅), and pyrosilicic acid (H₆Si₂O₇).
 56. The process of claim 47 wherein the acid catalyst comprises zirconium phosphate.
 57. The process of claim 47 wherein the acid catalyst is a sulfonated polystyrene divinylbenzene copolymer.
 58. The process of claim 47 wherein the acid catalyst is a tetrafluoroethylene-perfluoro[2-(fluorosulfonylethoxy)-propyl]vinylether polymer.
 59. The process of claim 47 wherein a purge stream from the reactor is further reacted to form a stream containing a peroxycarboxylic acid.
 60. The process of claim 59 wherein the peroxycarboxylic acid is at least one of peroctanoic acid and peroxymonosulfuric acid. 